Electromagnetic device



June 11, 1929. H. A. WALLACE ELECTROMAGNETIC DEVICE Filed April 50, 1926w 9 Q 5 W m i Q I n1 n D.-

INVENTOR Patented June 11, 1929.

UNITED STATES PATENT OFFICE.

HERBERT A. WALLACE, OF EDGEWOOD BOROUGH, PENNSYLVANIA, ASSIGNOR TO THEUNION SWITCH 8a SIGNAL COMPANY, OF SWISSVALE, PENNSYLVANIA, A CORPO-RATION OF PENNSYLVANIA.

ELECTROMAGNETIC DEVICE.

Application filed April 30, 1926.

My invention relates to electromagnetic devices, and particularly tomeans for ren dering the rate of operation of such devices inde pendentof temperature changes.

I will describe two forms of electromagnetic devices embodying myinvention. and will. then point out the novel features thereof inclaims.

In the accompanying drawings, Fig. 1 is a view of a retarded relayembodying my invention, the top plate, the base and a portion of themagnet being shown in section, Fig. 2 is a similar view of amodification also embodying my invention.

Similar reference characters refer to similar parts in both views.

Referring first to Fig. 1, the relay comprises a top plate 1, supportedupon a base designated generally by the reference character 2.. Mountedupon the top plate 1 is an electromagnet 3, comprising an iron core 4, awinding 5, a back strap 22 and a metallic sleeve 6. The sleeve 6 forms ashort eircuited conducting path about the core 4, to cause a slowrelease of the armature, after de-energization of the relay, in theusual manner.

Secured to the lower end of the core 4 1s a pole piece 7 from which thearmature 8 is pivotally suspended at pivot 9. The movement of thearmature 8 is limited by a stop member 10, this member being secured toa compensating rod 11 which is rigidly fastened to back strap 22. Therod 11 passes loosely through an aperture in plate 1 and is of materialhaving a smaller temperature coefficient of expansion than the materialof which the core 4. is made, for a purpose which will appearhereinafter. The stop member 10 carries a contact 12 which is securedthereto by an insulating member 13. The armature 8 carries the usualcontact bar 14 on which the movable contact 15 is mounted. The bar 14 issecured to armature 8 by insulating studs 19. The contact 12 iselectrically connected to a binding post 16,.and movable contact 15 iselectrically connected to a binding post 18 by means of contact bar 14:and flexible lead 17.

Energization of electromagnet 3 will cause armature 8 to be lifted untilit strikes the upper portion of stop member 10 and contacts 15 and 12will engage. When the electromagnet 3 is de-energized, the electromotiveforce induced in sleeve 6 will tend to keep the flux Serial No. 105,764.

in core 4.- constant so that the armature will not be released until theflux in core 4 falls below its critical value.

The time required for the relay to pick up may be made constant; byover-energizing it but the time required for the armature 8 to releaseafter de-energization of winding 5 depends mainly upon the resistance ofthe short-circuited sleeve 6, the percentage change in the winding 5being relatively small. It has been found that changes iii ambienttemperature affect the resistance of slcct e 6 so as to materially alterthe time required for the relay to release its armature under differenttemperature conditions. If a relay of this type is to be used where acon stant rate of release is necessary, some thermally responsive meansmust be provided for compensation.

If the sleeve 6 is made of copper, since copper has a positivetemperature coeflicient of resistance, a rise in temperature increasesthe resistance of the sleeve so that for a given current in the winding5 the current induced in sleeve 6 is materially lessened. A smallerinduced current in sleeve 6 produces a smaller flux so that the armature8 is released quicker at high temperatures than at low temperatures. Ifuniform retardation is to be secured at all temperatures, means must beprovided for varying the position of the armature so as to compensatefor temperature changes. The armature 8 must be moved closer to the core4: upon rise in temperature and moved away from the core upon fall intemperature.

One means of rendering the rate of operation of the relay independent oftemperature changes is shown in Fig. 1, wherein the stop member 10 forlimiting the extent of movement of armature 8 is secured to thecompensating rod 11. Rod 11 is made of a material which has a lowertemperature coeflicient of expansion than the iron core 4, for example,hard wood may be used. lVhen the temperature of sleeve 6 is increased,the core 4 expandsmore rapidly than rod 11 so that the air gap betweenpole piece 7 and armature 8 is decreased. A decrease in flux due toincrease in ambient temperature will be compensated for, by theshortening of the air gap, hence the length of time required forarmature 8 to be released, will be substan tially constant throughoutthe range for which the relay is calibrated.

sion so that an increase in temperature will move the free end upwardand a decrease in temperature will -move it downward. One end of thethermostat 20 is secured to the top plate 1 by means of a bolt 21, andthe free end carries the stop member 10. Any movement of the thermostatwill move the stop 10 and thus vary the air gap between pole piece 7 andarmature 8. As previously explained with reference to Fig. 1, thecompensating means has such characteristics that variations in thetemperature of sleeve 6 will not vary the time required for the relay todrop its armature, within the temperature range over which the relay iscalibrated.

lVhile I have shown and described but two forms of apparatus embodyingmy invention, it is understood that various changes and modificationsmay be made therein within the scope of the appended claims withoutdeparting from the spirit and scope of my invention.

Having thus described my invention, what I claim is: Y

1. An electromagnetic device comprising an armature, an electromagnetfor operating said armature, a short-circuited conductor on saidelectromagnet subject to temperature variations, a stop 'for saidarmature, and thermal responsive means for moving said stop tocompensate for temperature variations in the short circuited conductor.

2. An electromagnetic device comprising an electromagnet including ashort-circuited metallic sleeve mounted thereon, an armature controlledby said electromagnet, and temper ature controlled means to compensatefor changes in the retardation effect of the metallic sleeve duringtemperature variations in said sleeve.

3. A relay comprising a supporting plate, an electromagnet carried bysaid plate and having a short-circuited conductor in inductive relationtherewith, an armature, a stop for said armature, a contact on saidstop, a contact on the armature adapted to engage the contact on thestop, and thermal responsive means for changing the position of saidstop to compensate for the efiect of temperature variations in theshort-circuited conductor.

- 4. A relay comprising an armature having a contact thereon, anelectromagnet for moving said armature, a short-circuited conductor onsaid electromagnet, a stop for said armature, a contact mounted on saidstop and adapted for engagement with said first contact. and thermalresponsive means for moving the stop and the contact associatedtherewith.

5. An electromagnetic device comprising an armature, an electromagnetincluding an secured thereto, said member having a lower 7 temperatureco-eiiicient of expansion than said iron core and being constructed andarranged to co-operate with the iron core of the electromagnet tocompensate for temperature variations in the conducting sleeve.

6. An electromagnetic device comprising an armature, an electromagnetfor operating the armature, a conducting sleeve on the electromagnet andtemperature controlled means for adjusting the rate of operation of saidarmature to compensate for changes in temperature in the sleeve.

7. An electromagnetic device comprising an armature, a stop for saidarmature, an electromagnet having an iron core, a short circuited sleeveon said core, a back strap secured to said core and a temperaturecompensating rod secured to said back strap and carrying said stop.

8. An electromagnetic device comprising an armature, an electromagnetincluding an iron core and a back strap, a temperature compensating rodsecured to said back strap and mounted approximately parallel to theiron core of the electromagnet, and a stop for said armature secured tosaid rod.

In testimony whereof I affix my signature.

HERBERT A. WALLACE.

